Package on package structure and method for forming the same

Abstract

Some embodiments relate to a semiconductor device package, which includes a substrate with a contact pad. A non-solder ball is coupled to the contact pad at a contact pad interface surface. A layer of solder is disposed over an outer surface of the non-solder ball, and has an inner surface and an outer surface which are generally concentric with the outer surface of the non-solder ball. An intermediate layer separates the non-solder ball and the layer of solder. The intermediate layer is distinct in composition from both the non-solder ball and the layer of solder. Sidewalls of the layer of solder are curved or sphere-like and terminate at a planar surface, which is disposed at a maximum height of the layer of solder as measured from the contact pad interface surface.

What is claimed is: 
     
       1. A semiconductor device comprising a solder ball, comprising:
 a copper pad; 
 a copper ball disposed over an upper surface of the copper pad; 
 a layer of solder over an outer surface of the copper ball, the layer of solder having different annular thicknesses at different locations over the outer surface of the copper ball; and 
 an intermediate layer comprising nickel separating the copper ball and the layer of solder, wherein the intermediate layer has different annular thicknesses varying between 0.5 micrometers and 2 micrometers at different locations of the intermediate layer. 
 
     
     
       2. The semiconductor device of  claim 1 , wherein the different annular thicknesses vary between 0.8 micrometers and 1.4 micrometers at different locations of the intermediate layer. 
     
     
       3. The semiconductor device of  claim 1 , wherein the copper ball has a maximum width ranging between 200 micrometers and 250 micrometers. 
     
     
       4. The semiconductor device of  claim 1 , wherein the layer of solder comprises Sn or a solder alloy. 
     
     
       5. The semiconductor device of  claim 1 , further comprising:
 a package including a first semiconductor die; 
 a substrate, wherein the layer of solder has a first maximum width and attaches a lower surface of the package to an upper surface of the substrate; 
 a second semiconductor die arranged between the upper surface of the substrate and the lower surface of the package, and arranged to a side of the solder ball, 
 a bonding structure connecting the second semiconductor die to the substrate, wherein the bonding structure has a second maximum width that is less than the first maximum width. 
 
     
     
       6. The semiconductor device of  claim 5 , further comprising:
 a molding underfill layer disposed between the upper surface of the substrate and the lower surface of the package, and separating an upper surface of the second semiconductor die from the lower surface of the package. 
 
     
     
       7. A semiconductor device, comprising:
 a copper pad; 
 a copper core disposed over the copper pad; 
 an intermediate layer comprising nickel surrounding the copper core; and 
 a layer of solder comprising tin and disposed over an outer surface of the copper core, wherein the intermediate layer separates the layer of solder from the copper core and wherein the intermediate layer has different annular thicknesses at different locations of the intermediate layer. 
 
     
     
       8. The semiconductor device of  claim 7 , further comprising: a bonding layer coupling the copper core to the copper pad. 
     
     
       9. The semiconductor device of  claim 7 , wherein the different annular thicknesses vary between 0.8 micrometers and 1.4 micrometers at different locations of the intermediate layer. 
     
     
       10. The semiconductor device of  claim 7 , wherein the copper core has a maximum width ranging between 200 micrometers and 250 micrometers. 
     
     
       11. The semiconductor device of  claim 7 , wherein the layer of solder comprises Sn or a solder alloy. 
     
     
       12. The semiconductor device of  claim 7 , further comprising:
 a package including a first semiconductor die; 
 a substrate, wherein the layer of solder has a first maximum width and attaches a lower surface of the package to an upper surface of the substrate; 
 a second semiconductor die arranged between the upper surface of the substrate and the lower surface of the package, and arranged next to an outermost surface of the layer of solder; 
 a bonding structure connecting the second semiconductor die to the substrate, wherein the bonding structure has a second maximum width that is less than the first maximum width. 
 
     
     
       13. The semiconductor device of  claim 12 , further comprising:
 a molding underfill layer disposed between the upper surface of the substrate and the lower surface of the package, and separating an upper surface of the second semiconductor die from the lower surface of the package. 
 
     
     
       14. A semiconductor device, comprising:
 a substrate; 
 a package including a first semiconductor die disposed over an upper surface of the substrate; 
 a second semiconductor die arranged between the upper surface of the substrate and a lower surface of the package, 
 a solder ball coupling the upper surface of the substrate to the lower surface of the package, wherein the second semiconductor die is arranged to a side of the solder ball; 
 a bonding structure connecting the second semiconductor die to the substrate; 
 the solder ball comprising:
 a copper core; 
 a layer of solder over an outer surface of the copper core, wherein the layer of solder attaches the lower surface of the package to the upper surface of the substrate; and 
 an intermediate layer separating the copper core and the layer of solder; 
 wherein the layer of solder has a first annular thickness on a first portion of the intermediate layer and has a second annular thickness on a second portion of the intermediate layer, the second annular thickness being greater than the first annular thickness. 
 
 
     
     
       15. The semiconductor device of  claim 14 , wherein the copper core, the intermediate layer, and the layer of solder each have a center region that lies along a common axis which extends perpendicularly though the upper surface of the substrate. 
     
     
       16. The semiconductor device of  claim 15 , wherein the intermediate layer has different annular thicknesses varying between 0.5 micrometers and 2 micrometers at different locations of the intermediate layer. 
     
     
       17. The semiconductor device of  claim 16 , wherein the different annular thicknesses vary between 0.8 micrometers and 1.4 micrometers at the different locations of the intermediate layer. 
     
     
       18. The semiconductor device of  claim 14 , wherein the copper core has a maximum width ranging between 200 micrometers and 250 micrometers. 
     
     
       19. The semiconductor device of  claim 14 , further comprising:
 a bonding layer coupling the copper core to a contact pad. 
 
     
     
       20. The semiconductor device of  claim 14 , wherein the intermediate layer has different annular thicknesses varying between 0.5 micrometers and 2 micrometers at different locations of the intermediate layer.